This invention relates to direct injection of fuels in internal combustion engines. More particularly, the invention relates to an apparatus and method for direct injection of fuels into spark-ignition internal combustion engines. The invention also relates to a combined fuel injection and ignition means for spark-ignition internal combustion engines.
For a spark-ignition internal combustion engine having fuel directly injected into a combustion chamber, it is highly desirable to introduce the fuel into the combustion chamber in a form conducive to effect reliable and repeatable ignition. Typically, this requires that fuel droplets present at a spark gap in the combustion chamber are of a suitable size to provide favourable ignition conditions, and to avoid both quenching of either one or both of the electrodes which define the spark gap and insulation of either one or both of the electrodes by the fuel. This requirement can in certain applications be difficult to achieve, particularly where the fuel injector is combined into a single assembly with the ignition means.
Examples of arrangements involving combined fuel injection and ignition means are disclosed in U.S. Pat. No. 4,967,708 (Under et al), EP 0 632 198 (Suzuki), U.S. Pat. No. 5,497,744 (Nagaosa et al), and U.S. Pat. No. 5,730,100 (Bergsten).
Bergsten discloses an injector arrangement for injection of fuel and ignition of the resultant air-fuel mixture in the combustion chamber of a reciprocating-piston engine. The injector arrangement includes a valve housing, a valve needle and a valve element, all of which are made of electrically conductive material and which together form an electrode positioned centrally in the injector arrangement, so constituting a single-pole ignition plug. The second electrode is operatively attached to the piston or to the cylinder in which the piston reciprocates. With this arrangement, the injector delivers fuel into the combustion chamber, and co-operation between the electrode on the injector and the second electrode within the combustion chamber creates a spark gap at which an ignition spark can be established in timed sequence with operation of the engine. This arrangement enables fuel to be delivered into the combustion chamber as a single fluid in the form of a spray or cloud of fuel droplets, but not necessarily in a manner which regulates the dispersion and flow of fuel to the spark gap so as to facilitate a reliable ignition process and avoid quenching of the electrodes.
Further, due to physical limitations, it is often difficult if not impossible to arrange the spark gap of a suitable ignition means at the most optimum point within the combustion chamber. For example, in certain applications the optimum area for ignition may be xe2x80x98out of reachxe2x80x99 of a conventional ignition means. This may hence require the use of specially modified ignition means such as long reach spark plugs or unique orientations thereof within the cylinder head of an engine. In turn, this may result in increased cost and other engineering and durability issues which may be difficult to overcome.
It is against this background, and the problems and difficulties associated therewith, that the present invention has been developed. Specifically, it is an object of the present invention to provide a fuel delivery injector which delivers fuel to a spark gap in a manner which provides conditions conducive to effect reliable ignition.
The present invention provides a fuel delivery injector for a spark-ignition internal combustion engine, the fuel delivery injector comprising means defining a flow path for delivery of a fuel entrained in a gas to a combustion chamber of the engine, the flow path having a delivery port through which the fuel is delivered into the combustion chamber as a spray of fuel droplets and vapour, the delivery port being defined between a valve seat and a valve member movable with respect to the valve seat for opening and closing the delivery port, the delivery injector being configured to influence the trajectory of the fuel spray whereby smaller fuel droplets and vapour in the fuel spray are caused to flow towards a spark gap in close proximity to the downstream end of the delivery port and whereby larger fuel droplets are not so caused to flow towards the spark gap.
Preferably, the fuel delivery injector includes a flow control means disposed outwardly of the delivery port in the direction of issuance of the fuel spray, the flow control means being configured and positioned to influence the trajectory of the fuel spray whereby smaller fuel droplets and vapour in the fuel spray are caused to flow towards the spark gap in the vicinity of the control means.
With this arrangement, the spark gap is able to be located in the region downstream of the delivery port where the small fuel droplets and vapour are more prevalent, this area and such conditions being more favourable to reliable and repeatable ignition. In effect, the larger fuel droplets which are likely to inhibit the ignition process at the spark gap are separated from the smaller droplets in the gaseous stream, the larger droplets continuing to follow a trajectory established upon exit from the delivery port by virtue of their momentum.
Alternatively, or additionally, the flow control means may comprise or further comprise the delivery port.
Preferably, the flow control means comprises a flow control projection supported on the valve member and extending outwardly therefrom beyond the delivery port. The smaller droplets and vapour are guided by the profile of the projection in accordance with the Coanda Effect. That is, the small droplets and vapour are drawn inwards towards the surface of the projection such that a certain degree of xe2x80x98necking inxe2x80x99 of the fuel spray occurs. It should however be noted that, in certain applications, a similar effect may result even though there is no flow control projection provided downstream of the valve member. In such cases, it is believed that the small fuel droplets and vapour are drawn inwardly following their delivery into the combustion chamber due to the presence of a generally low pressure area immediately beneath the valve member of the fuel delivery injector.
The projection may, for example, have a profile as disclosed in U.S. Pat. No. 5,551,638, or U.S. Pat. No. 5,833,142, both of which have been assigned to the Applicant and the contents of which are incorporated herein by way of reference. The projection may be formed integrally with the valve member, or it may be detachable therefrom, such as for example, by way of a screw-threaded connection.
Where the injector forms part of a combined injection and ignition means, the control projection may define a first electrode which co-operates with a second electrode to define the spark gap. The first electrode defined by the control projection is preferably a primary electrode, in which case the second electrode defines a secondary electrode. The two electrodes can be so disposed relative to one another such that the spark gap defined therebetween can provide either a radial gap or an axial gap. If desired, there may be more than one said second electrode, in which case the second electrodes may conveniently be circumferentially spaced about the primary or central electrode defined by the control projection. In certain applications where a projection is not provided downstream of the valve member, or as an alternative arrangement where a control projection does exist, the valve member itself may be configured as the first electrode with the spark gap being provided between the valve member of the injector and the second electrode(s).
By having the spark gap defined by the projection or the valve member, the location of the spark gap within the region of small fuel droplets and vapour formed by the fuel delivery injector is effectively ensured. This is due to the effect of the delivery port and/or the flow control projection which facilitate the smaller fuel droplets and vapour in the fuel spray being attracted to the area in close proximity to the downstream end of the delivery port where the spark gap is arranged.
In the case where the spark gap is configured as a radial gap between the projection or valve member and the secondary electrode(s), certain benefits may be realised for the injector. Firstly, the combined injection and ignition means will generally be slightly shorter over its entire length as no element needs to be provided downstream of the control projection to provide the spark gap. Secondly, as a range of, or changing profile of air-fuel ratios, is likely to exist substantially perpendicularly to the direction of fuel flow into the cylinder, a spark across a radial gap is potentially more likely to traverse across a greater number of these air-fuel ratios and hence the likelihood of ignition of the fuel-air charge occurring is increased. This is particularly applicable in stratified charge or lean burn engines where such a range of air-fuel ratios are likely to exist in the fuel spray delivered into the combustion chamber by the injector.
Preferably, ignition of the fuel-air charge in the combustion chamber is able to occur directly off the fuel spray which issues from the delivery injector. That is, it is not necessary for the fuel spray to be reflected or deflected off other components, such as for example, a piston bowl, in the combustion chamber before ignition can be effected. Conveniently, ignition occurs off the inner part of the fuel spray. That is, ignition is effected in the area immediately adjacent the control projection or the central region of the combustion chamber as opposed to the outer parts or periphery of the fuel spray.
Preferably, the fuel delivery injector is arranged to deliver fuel entrained in gas directly into the combustion chamber of the engine. Such gas or air-assisted injection is particularly conducive to the establishment of a stratified fuel-air distribution in the combustion chamber. Conveniently, the delivery injector is of the outwardly opening or poppet type. Preferably, the delivery port comprises an annular passage divergent in the direction of flow of the fuel entrained in the gas. It is particularly advantageous for the annular passage defining the delivery port to be of a construction which includes a constricted section defining a minimum choke area and a divergent section downstream of the constricted section defining a divergent nozzle. Such a construction assists in the creation of small droplets of fuel in the fuel spray exiting from the injector. This construction may be achieved by providing the valve seat as an annular surface of frusto-conical form so as to provide the divergent characteristic. The valve member may be provided with a sealing face of arcuate formation confronting the valve seat.
The fuel delivery injector may also include a valve housing defining a valve having a valve stem, the valve member being mounted on one end of the valve stem. The valve stem may be accommodated within a bore within the valve housing. Conveniently, the valve seat is provided about the bore at the combustion chamber end of the valve housing.
The invention also provides a combined fuel injection and ignition means for a spark-ignition internal combustion engine, the combined fuel injection and ignition means comprising means defining a flow path for delivery of a fuel entrained in a gas to a combustion chamber of the engine, the flow path having a delivery port through which the fuel is delivered into the combustion chamber as a spray of fuel droplets and vapour, the delivery port being defined between a valve seat and a valve member movable with respect to the valve seat for opening and closing the delivery port, a first electrode for co-operation with a second electrode to form a spark gap, and a flow control means for influencing the trajectory of the fuel spray issuing from the delivery port whereby smaller fuel droplets and vapour in the fuel spray are caused to flow towards the spark gap and whereby larger fuel droplets are not so caused to flow towards the spark gap.
The flow control means may comprise a flow control projection provided on the valve member and extending outwardly of the delivery port in the direction of issuance of the fuel spray. Alternatively, or additionally, the flow control means may comprise or further comprise the delivery port.
The second electrode may form part of the combined fuel injection and ignition means, or it may exist separately thereof. Where the second electrode is provided as part of the combined fuel injection and ignition means, the second electrode is preferably configured and positioned to provide a radial spark gap. Hence, such a dual pole ignition plug would enable ignition to be effected directly off the inner region of the issuing fuel spray.
The invention also provides a combined fuel injection and ignition means for a spark-ignition internal combustion engine, the combined fuel injection and ignition means comprising means defining a flow path for delivery of a fuel entrained in a gas to a combustion chamber of the engine, the flow path having a delivery port through which the fuel is delivered into the combustion chamber as a spray of fuel droplets and vapour, the delivery port being defined between a valve seat and a valve member movable with respect to the valve seat for opening and closing the delivery port, a flow control projection arranged on the valve member and extending outwardly of the delivery port in the direction of issuance of the fuel spray, the flow control projection defining an electrode which in co-operation with a further electrode forms a spark gap, the delivery port and/or the control projection being configured and positioned to influence the trajectory of the fuel spray whereby smaller fuel droplets and vapour in the fuel spray are caused to flow towards the spark gap and whereby larger fuel droplets are not so caused to flow towards the spark gap.
The invention also provides a method of injecting fuel into an internal combustion engine having a combustion chamber and a spark gap for spark-ignition of the fuel delivered into the combustion chamber, the method comprising the acts of: delivering a metered quantity of fuel entrained in a gas to the combustion chamber through a selectively openable delivery port to provide a fuel spray issuing from the port when opened; and controlling the fuel spray to influence fuel vapour and smaller fuel droplets to flow towards the spark gap while not so influencing larger droplets whereby the larger droplets continue on trajectories which do not lead to the spark gap.
The fuel spray may be so controlled by subjecting it to a flow control means positioned downstream of the delivery port. The fuel spray may also or alternatively be so controlled by virtue of the configuration of the delivery port.